U.S. Pat. No. 5,861,714 and U.S. Pat. No. 5,742,123 disclose a high-pressure discharge lamp in which a ceramic discharge vessel uses an axially layered cermet part for sealing at its ends.
In U.S. Pat. No. 5,742,123, a tungsten rod having a screw thread is fitted into a cermet part, the individual layers of which increase outward in their thickness. A platinum solder covers a flange on the cermet part. The number of layers is about 10. The first layer is placed directly onto the end of the discharge vessel, and the last layer is hermetically connected to the flange and the tungsten rod by means of the platinum solder.
In U.S. Pat. No. 5,861,714, the sealing between the last layer and the feed-through is produced by direct sintering and optionally assistance by means of glass solder. In both cases, the cermet parts are difficult to produce. The lifetime is unsatisfactory owing to the small number of stages and owing to the concept of sealing the feed-through in the last layer.